Dynamic and static muon-spin relaxation observed above and below the spin-crossover in Fe(II) complexes

Abstract
The spin-crossover phenomenon is a cooperative low-spin (LS) to high-spin (HS) transition which can be initiated using temperature or light irradiation. We have used muon-spin relaxation ( SR) to study this transition in two salts which show this effect. SR provides local magnetic information and hence a means of examining this transition from a local perspective. For both salts, the LS phase gives rise to root-exponential relaxation which we associate with a dilute distribution of fluctuating moments resulting from incomplete spin crossover. The low temperature HS fraction which remains is small but can be altered by rapid cooling. We relate the observed muon relaxation to the underlying fluctuating moment distribution and compare our results to Monte-Carlo simulations of these distributions.